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Old 11th February 2014, 01:37 AM   #1
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Default help with Onkyo 7.1 repair

I recently picked up an onkyo ht-r667 to try to repair. It powers on but turns back off right when the relays click with a blinking standby light (i assume thats protection mode.) at first i suspected a damaged dsp because it seems like caps were added to the dsp to fix the hdmi problems that is apparently common to these units. But i found a pair of shorted output transistors, so i have removed them. Can i power on the receiver without the transistors in place to see if it will go into protect? I want to be sure they are the cause before i try to locate a replacement. i also have plenty of MN2488 + MP1620 in my parts bin, could i drop those in as temporary replacements to see if it will power on? the originals are c5242 + a1962. Thanks for any help!
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Old 11th February 2014, 04:14 AM   #2
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Resoldering might solve the problem.

Gajanan Phadte
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Old 11th February 2014, 01:32 PM   #3
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Originally Posted by gmphadte View Post
Resoldering might solve the problem.

Gajanan Phadte
It looks like all the solder connections are good on this receiver. I found two shorted output transistors. Can i power it up without the output transistors or will that damage something? Thanks!
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Old 11th February 2014, 07:03 PM   #4
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From a lot of others on this thread doing the same thing... I would say try it. With the shorts gone the power transformer can turn on the way it is suppose to.
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Old 11th February 2014, 09:48 PM   #5
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my experience with Onkyo has been that if the outputs are shorted, so are the drivers, and possibly the VAS and it's current source. there will probably be a bunch of those little flameproof resistors burned open too..... some Onkyo receivers i've seen may have damage all the way back to the diff amps. DON'T use the sony transistors to replace the outputs, even for testing. those MN and MP transistors are darlingtons. they will not bias properly, and their huge junction capacitance may make the amp channel oscillate.
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Old 11th February 2014, 11:06 PM   #6
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Originally Posted by unclejed613 View Post
my experience with Onkyo has been that if the outputs are shorted, so are the drivers, and possibly the VAS and it's current source. there will probably be a bunch of those little flameproof resistors burned open too..... some Onkyo receivers i've seen may have damage all the way back to the diff amps. DON'T use the sony transistors to replace the outputs, even for testing. those MN and MP transistors are darlingtons. they will not bias properly, and their huge junction capacitance may make the amp channel oscillate.
Thanks! i checked other small transistors that were close to the burned channel and none seem to be shorted. If i power on with no output transistors will that damage anything? I want to make sure that was the only cause of the protect mode ( the dsp may still be bad)
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Old 11th February 2014, 11:57 PM   #7
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I looked over the schematics, and the blown channel is one of the surround channels, I plan to use the unit in stereo or 3 channel mode, can it function without that channel?
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Old 12th February 2014, 08:45 AM   #8
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Yes, it will work provided you remove the faulty transistors. But then, you will have take care of any supervisory connection that detects fault.

In general, there will be a dc detection circuit that gets its input from the output of a power amp. This will be there for all the channels. Connecting the unused (without transistors) output to ground may be all that is needed. Will have to see the schematic to be sure.

Gajanan Phadte
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Old 12th February 2014, 04:32 PM   #9
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Originally Posted by gmphadte View Post
Yes, it will work provided you remove the faulty transistors. But then, you will have take care of any supervisory connection that detects fault.

In general, there will be a dc detection circuit that gets its input from the output of a power amp. This will be there for all the channels. Connecting the unused (without transistors) output to ground may be all that is needed. Will have to see the schematic to be sure.

Gajanan Phadte
Thanks! hopefully thats all there is too it, i do not plan on using surround channels. I have attached the schmatic for the damaged channel. Thanks.Untitled.png
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Old 12th February 2014, 04:41 PM   #10
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if you connect a 1500 ohm/2W resistor between each B-E connection of the place where the output transistors go, it will close the feedback loop and you can test the channel that way. you can apply signal to the channel and get a waveform out.... but make sure you don't connect a load.....
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